--> Development of a Novel Method to Analyze Saturated Hydrocarbon in Crude Oil by SPME

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Development of a Novel Method to Analyze Saturated Hydrocarbon in Crude Oil by SPME

Abstract

Using column chromatography-GC-FID to analyze saturated hydrocarbon in crude oil is time consuming. A time-saving (the entire process takes less than three hours) headspace solid-phase microextraction (SPME)-GC-FID method to monitor saturated hydrocarbon in crude oil was developed and the conditions for maximum yield were determined. Based on the optimization of experimental conditions, the optimum laboratory procedure for SPME saturated hydrocarbon monitoring was established as follows: the sample of crude oil was diluted in a 15 ml clean vial by pure water; the fiber was exposed to the headspace above the sample for 25 min at 50 C, with concentration 0.2 mg/mL; then the fiber was inserted into the heated GC injection port (290 C) to desorb for 5 min. The oven temperature programme was 50 C for 1 min then 50–280 C at 3 C / min and at last 280 C for 10 min. Subsequently, a crude oil sample from Biyang Depression was analyzed under the optimum conditions. The diagnostic ratios (Pr/Ph, Pr/n-C17, Ph/n-C18, and OEP) calculated from SPME were 0.72, 0.42, 0.58 and 1.0 respectively, close with those obtained from column chromatography (0.72, 0.35, 0.52 and 0.99). Then the other four samples of crude oil from Biyang Depression were analyzed by SPME, so as to make a quantitative comparison between SPME and column chromatography. Results shows that Pr/n-C17 obtained from SPME and column chromatography respectively have a linear relationship as well as Ph/n-C18, while Pr/Ph obtained from SPME and column chromatography respectively have a quadratic relationship as well as OEP. Additionally, the transformation formulas of ratios calculated from SPME methodology and column chromatography methodology respectively were established. And the correlation coefficients (R2) including Pr/n-C17 obtained from column chromatography as a function of Pr/n-C17 obtained from SPME (R2=0.93), Ph/n-C18 obtained from column chromatography as a function of Ph/n-C18 obtained from SPME (R2=0.98), Pr/Ph obtained from column chromatography as a function of Pr/Ph obtained from SPME (R2=0.99) and OEP obtained from column chromatography as a function of OEP obtained from SPME (R2=0.86) were all greater than 0.85, which shows the transformation formulas are reliable. So SPME can be used to analyze saturated hydrocarbon in crude oil. In addition, this novel method also has a certain application prospect in oilfield water detection, crude oil pollution assessment and field test of crude oil components.